borg repair: deal with corrupt hints file

[ThomasWaldmann]

see: jborg/attic#375

todo:

• reproduce (do we get same traceback still?)
• can borg repair fix that?

[enkore]

The segment index / hints files are automatically regenerated (no check needed) if missing. So, just wrap the reading part in a try..except, log & delete & regenerate them?

Since that does require a lot of IO (skimming all segment files), and normally shouldn't happen => log level warning.

EDIT:

• Corrupted index; borg.hashindex will raise "Exception('hashindex_read failed')"; Too broad to catch sanely, better narrow that. RuntimeError or lower
• Something wrong with the hints file; raises msgpack.exceptions.XXX, but only if that file is actually used (Repository transaction created)

[x] Reproduced, changing tag question -> enhancement.

WIP

[enkore]

Fixed in #858, further protections discussed in #1101